Fix zero streams after max_streams_to_max_threads_ratio applied

Set at least one stream for reading in case there are zero planned
streams after applying `max_streams_to_max_threads_ratio` setting.

Author: korowa

src/Interpreters/InterpreterSelectQuery.cpp

@@ -2652,8 +2652,6 @@ void InterpreterSelectQuery::executeFetchColumns(QueryProcessingStage::Enum proc
     else if (storage)
     {
         /// Table.
-        if (max_streams == 0)
-            max_streams = 1;
 
         /// If necessary, we request more sources than the number of threads - to distribute the work evenly over the threads.
         if (max_streams > 1 && !is_sync_remote)
@@ -2668,6 +2666,9 @@ void InterpreterSelectQuery::executeFetchColumns(QueryProcessingStage::Enum proc
                     streams_with_ratio);
         }
 
+        if (max_streams == 0)
+            max_streams = 1;
+
         auto & prewhere_info = analysis_result.prewhere_info;
 
         if (prewhere_info)

src/Planner/PlannerJoinTree.cpp

@@ -771,9 +771,6 @@ JoinTreeQueryPlan buildQueryPlanForTableExpression(QueryTreeNodePtr table_expres
                     "Setting 'max_block_size' cannot be zero");
         }
 
-        if (max_streams == 0)
-            max_streams = 1;
-
         /// If necessary, we request more sources than the number of threads - to distribute the work evenly over the threads
         if (max_streams > 1 && !is_sync_remote)
         {
@@ -787,6 +784,9 @@ JoinTreeQueryPlan buildQueryPlanForTableExpression(QueryTreeNodePtr table_expres
                     streams_with_ratio);
         }
 
+        if (max_streams == 0)
+            max_streams = 1;
+
         if (table_node)
             table_expression_query_info.table_expression_modifiers = table_node->getTableExpressionModifiers();
         else

tests/queries/0_stateless/03402_zero_streams_after_max_streams_to_max_threads_ratio.reference

@@ -0,0 +1,7 @@
+49.5
+49.5
+49.5
+
+0
+0
+0

tests/queries/0_stateless/03402_zero_streams_after_max_streams_to_max_threads_ratio.sql

@@ -0,0 +1,16 @@
+DROP TABLE IF EXISTS 03402_data;
+
+CREATE TABLE 03402_data (id UInt32) ENGINE = MergeTree ORDER BY id;
+INSERT INTO 03402_data SELECT * FROM numbers(100);
+
+SELECT avg(id) FROM 03402_data SETTINGS max_threads = 4, max_streams_to_max_threads_ratio = 0;
+SELECT avg(id) FROM 03402_data SETTINGS max_threads = 0, max_streams_to_max_threads_ratio = 0;
+SELECT avg(id) FROM 03402_data SETTINGS max_threads = 2, max_streams_to_max_threads_ratio = 0.2;
+
+SELECT '';
+
+SELECT id FROM 03402_data ORDER BY id LIMIT 1 SETTINGS max_threads = 4, max_streams_to_max_threads_ratio = 0;
+SELECT id FROM 03402_data ORDER BY id LIMIT 1 SETTINGS max_threads = 0, max_streams_to_max_threads_ratio = 0;
+SELECT id FROM 03402_data ORDER BY id LIMIT 1 SETTINGS max_threads = 2, max_streams_to_max_threads_ratio = 0.2;
+
+DROP TABLE 03402_data;